The tender interactions between human mothers and their newborn babies may have deep evolutionary roots: a new study found that rhesus macaque monkey mothers engage in strikingly similar behavior with their infants.

The researchers found that the mothers would gaze intently at their newborns, sometimes even taking their baby’s face with their hands and gently pulling it towards them to get an even closer look. They would also engage in “lipsmacking” – an affectionate form of expression, where the macaques rapidly open and close their mouths [BBC News]. Several videos taken by the researchers show that just like human babies, the infant monkeys responded to their mothers by mimicking their facial expressions and returning their stares.

Lead researcher Pier Ferrari also observed another suggestive gesture on the part of the macaque moms: “They also touch the infant’s face with their mouths – as if they are trying to remove something. And this very much resembles the kiss that we have in our own species. Possibly the evolution of the kiss might have originated from this kind of interaction” [BBC News], he speculated.

The behavior only lasted for the first month of each infant’s life, according to the study in Current Biology, and then it stopped abruptly–in fact, among adult monkeys making direct eye contact is considered an aggressive act. Ferrari says the maternal behavior may quickly fade because one-month-old monkeys are rapidly gaining independence and becoming more interested in interacting with their peers.